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5G NR Physical Channels and Transport Channels

Transport channels and physical channels are not the same thing in 5G NR. Transport channels are the service interface between MAC and PHY, while physical channels are the actual radio-interface channels used over the air.

This page explains the transport-channel set, the physical-channel set, and the mapping between them. It also shows which physical channels do not come from transport channels and therefore need to be read differently in traces and procedure analysis.

Technology 5G NR
Area PHY channel hierarchy and transport-to-physical mapping
Main specs 3GPP TS 38.300, 38.202, 38.211
Release Release 18
Transport side BCH, DL-SCH, PCH, UL-SCH, RACH, SL-BCH, SL-SCH
Physical side PBCH, PDSCH, PDCCH, PUSCH, PUCCH, PRACH, PSBCH, PSCCH, PSSCH, PSFCH
Why it matters This is the bridge between MAC-delivered transport data and real over-the-air channels.

Contents

  1. Overview
  2. Where transport and physical channels fit
  3. Transport channels
  4. Physical channels
  5. Transport-to-physical mapping
  6. Where the mapping appears in real procedures
  7. Troubleshooting
  8. References
  9. FAQ

Overview

The channel hierarchy in NR is easiest to read as a layered chain: logical channels describe information type, transport channels describe how MAC presents data to PHY, and physical channels describe the actual radio channel used for transmission and reception.

This matters because trace analysis often mixes the terms. A paging event may be described as PCH on the transport side and PDSCH on the physical side. Both statements can be correct, but they refer to different layers of the same delivery path.

Where transport and physical channels fit

NR channel hierarchy Logical channels above MAC, transport channels between MAC and PHY, and physical channels at the air interface. NR channel hierarchy Logical channels BCCH, PCCH, CCCH, DCCH, DTCH Transport channels BCH, DL-SCH, PCH, UL-SCH, RACH Physical channels PBCH, PDSCH, PUSCH, PRACH, PDCCH MAC maps logical channels to transport channels PHY maps transport channels to physical channels

MAC is the layer that maps logical channels onto transport channels. PHY is the layer that takes transport channels and realizes them on physical channels. That is why this page belongs in the PHY section while still linking closely to the MAC channel page.

Transport channels

Transport channels are the channels seen at the MAC-PHY boundary. They describe the way data is transferred to PHY, but they are not yet the over-the-air channel names.

Transport channel Direction Purpose Notes
BCH Downlink Broadcast system information for basic cell access Associated with broadcast delivery and PBCH on the physical side
DL-SCH Downlink Main downlink transport channel for dedicated and shared data delivery Used widely for control-plane and user-plane delivery through PDSCH
PCH Downlink Paging transport channel Paging transport still reaches the air interface through PDSCH in NR
UL-SCH Uplink Main uplink transport channel for data and related uplink delivery Mapped to PUSCH
RACH Uplink Random access transport channel Mapped to PRACH for preamble-based access
SL-BCH Sidelink Sidelink broadcast transport channel Mapped to PSBCH
SL-SCH Sidelink Sidelink shared transport channel Used for sidelink data delivery with associated sidelink control context

NR does not define separate downlink transport channels for physical control delivery like PDCCH or uplink control delivery like PUCCH. Those are physical-control paths, not transport-channel paths.

Physical channels

Physical channels are the actual channels used on the air interface. Some carry transport channels, while some carry control information directly at PHY.

Physical channel Direction Main role Reference page
PBCH Downlink Broadcast channel for the MIB and basic broadcast delivery PBCH
PDSCH Downlink Main downlink shared physical channel PDSCH
PDCCH Downlink Downlink control delivery through DCI PDCCH
PUSCH Uplink Main uplink shared physical channel PUSCH
PUCCH Uplink Uplink control feedback channel PUCCH
PRACH Uplink Random access preamble channel PRACH
PSBCH Sidelink Sidelink broadcast physical channel SSB
PSCCH Sidelink Sidelink control channel Sidelink MAC
PSSCH Sidelink Sidelink shared physical channel Sidelink MAC
PSFCH Sidelink Sidelink feedback channel Sidelink MAC

Transport-to-physical mapping

NR transport and physical channel mapping Downlink, uplink, and sidelink mapping between transport channels and physical channels. Transport-to-physical mapping at a glance Transport channels Physical channels BCH DL-SCH / PCH UL-SCH RACH SL-BCH / SL-SCH PBCH PDSCH PUSCH PRACH PSBCH / PSSCH PDCCH, PUCCH, PSCCH, PSFCH do not come from transport channels
Transport channel Mapped physical channel Direction Reading notes
BCH PBCH Downlink Broadcast transport is realized on the physical broadcast channel.
DL-SCH PDSCH Downlink Main downlink transport is delivered on the physical downlink shared channel.
PCH PDSCH Downlink Paging is a transport-channel concept, but the physical delivery path is still PDSCH.
UL-SCH PUSCH Uplink Main uplink transport is delivered on the physical uplink shared channel.
RACH PRACH Uplink Random access preamble transmission uses PRACH.
SL-BCH PSBCH Sidelink Sidelink broadcast transport maps to the sidelink broadcast physical channel.
SL-SCH PSSCH Sidelink Sidelink shared transport is delivered on PSSCH, with associated sidelink control carried on PSCCH.

Physical channels without a transport-channel counterpart

Physical channel Why it stands alone Reference page
PDCCH It carries downlink control information directly at PHY rather than carrying a transport channel. PDCCH
PUCCH It carries uplink control information directly at PHY rather than carrying a transport channel. PUCCH
PSCCH It carries sidelink control directly and is read together with sidelink shared delivery. Sidelink MAC
PSFCH It carries sidelink feedback at PHY and is not a transport-channel mapping case. Sidelink MAC

Where the mapping appears in real procedures

Procedure area Transport view Physical view
Initial access BCH and RACH PBCH and PRACH
Paging PCH PDSCH, typically scheduled with PDCCH
Downlink data DL-SCH PDSCH, scheduled with PDCCH
Uplink data UL-SCH PUSCH, with control support from PUCCH or PUSCH-carried UCI
Random access RACH PRACH
Sidelink data SL-SCH PSSCH with associated PSCCH control

In call-flow reading, transport channels explain what is being moved between MAC and PHY. Physical channels explain how that content actually appears on the radio interface.

Troubleshooting

Common mistakes

  • treating transport-channel names and physical-channel names as interchangeable
  • assuming paging has a dedicated physical channel instead of reading it as PCH on transport side and PDSCH on physical side
  • assuming every physical channel must have a transport-channel counterpart
  • forgetting that PDCCH and PUCCH are physical-control channels, not transport-channel mappings
  • reading sidelink delivery without separating PSSCH shared delivery from PSCCH control

Troubleshooting clues

Symptom What to check Why
Paging interpretation looks wrong Separate PCH from PDSCH and check the PDCCH scheduling context Paging is a transport-channel concept, but delivery still happens through physical shared data resources.
Uplink issue is blamed on PUCCH when the problem is data delivery Separate UL-SCH on PUSCH from standalone PUCCH control PUSCH carries transport data, while PUCCH carries control feedback.
Broadcast and synchronization are mixed together Separate BCH/PBCH from SSB and other physical signals Not every important PHY structure is a physical channel.
Sidelink path is unclear Separate SL-SCH shared delivery from PSCCH and PSFCH control feedback Sidelink uses its own shared, control, broadcast, and feedback paths.

References

  • 3GPP TS 38.300 - NR overall description, including the NR channel model and channel sets
  • 3GPP TS 38.202 - NR services provided by the physical layer, including transport-channel associations
  • 3GPP TS 38.211 - NR physical channels and modulation
  • 3GPP TS 38.321 - NR MAC protocol specification, for logical-to-transport channel context

FAQ

What is the difference between a transport channel and a physical channel in 5G NR?

A transport channel is the PHY service seen by MAC, such as DL-SCH or UL-SCH. A physical channel is the actual over-the-air channel used on the radio interface, such as PDSCH, PUSCH, PDCCH, or PRACH.

Does every physical channel come from a transport channel?

No. PDCCH, PUCCH, PSCCH, and PSFCH are physical-control channels and do not have a transport-channel counterpart.

Which physical channel carries DL-SCH in 5G NR?

DL-SCH is carried on PDSCH.

Which physical channel carries UL-SCH in 5G NR?

UL-SCH is carried on PUSCH.

What is the mapping for BCH and RACH in 5G NR?

BCH maps to PBCH, and RACH maps to PRACH.

Related Content

  • 5G NR PHY Overview Use the PHY hub for the wider Layer 1 view around channels, signals, numerology, and procedures.
  • Logical Channels and Transport Channels Read the MAC-side view of channel hierarchy and logical-to-transport mapping.
  • 5G NR PDCCH Open the dedicated reference page for the physical downlink control channel.
  • 5G NR PDSCH See how DL-SCH and PCH payloads are delivered on the physical downlink shared channel.
  • 5G NR PUSCH See how UL-SCH payloads are delivered on the physical uplink shared channel.
  • 5G NR PUCCH Review the uplink control channel that does not come from a transport channel.
  • 5G NR PRACH Follow how the random access transport channel reaches the air interface.
  • 5G NR SSB Separate physical channels from synchronization and broadcast signal blocks.